It is known that luminous display devices such as signs having symbols and/or graphics elements such as images can be made out of a thin support or substrate which may be plane, such as a sheet or a panel of translucent or transparent material, and which is lighted via the edge of the support by means of a light source such as a fluorescent tube; one of the main faces of the support may have zones of shapes that correspond to symbols (digits or letters in particular) which are etched or frosted by sand-blasting so as to appear brighter than the remainder of the main face of the support.
The problem encountered in that type of device is the problem of non-uniform lighting: zones far away from the light source are darker; it also often happens that shadows can be seen that the frosted zones cast into other zones of the support.
Pat. No. EP 549 679 describes a sign comprising a light-transmitting sheet which is side-lighted and which has two opposite faces each having dots applied thereto; according to that document, in order to obtain regular lighting of the sign, the dots are etched, painted, or printed, and form a matrix substantially covering the two main surfaces of the sheet; nevertheless, it has been observed that that technique does not provide entire satisfaction.